Li4Ti5O12, Li(4-α)ZαTi5O12 or Li4ZβTi(5-βO12 particles, processes for obtaining same and use as electrochemical generators

ABSTRACT

A process for synthesizing particles of an oxide corresponding to a formula selected from: Li 4 Ti 5 O 12 ; Li (4-α) Z β Ti 5 O 12 ; and Li 4 Z α Ti (5-β) O 12 , said process including the steps of: a) preparing an intimately dispersed ternary mixture of TiO x —Li Z Y-carbon, wherein x is a number between 1 and 2, z is 1 or 2, Y is a radical chosen from the group consisting of CO 3 , OH, O and TiO 3  or a mixture thereof, and the carbon is a carbon powder selected from the group consisting of natural or artificial graphite, carbon black, Shawinigan black, Ketjen black and cokes; b) heating the dispersion at a temperature of between 400 and 1,000° C.; and c) if appropriate, adding a source of at least one metal Z to the ternary mixture, wherein the operating conditions are chosen in such a way as to yield a conversion of the initial products respectively into Li 4 Ti 5 O 12 , Li (4-α) Z α Ti 5 O 12 , Li 4 Z β Ti (5-β) O 12 .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/830,240, filed Apr. 23, 2004, which is a continuation of U.S.application Ser. No. 10/432,999, filed May 29, 2003, which is a §371national stage application of International Application No.PCT/CA01/01714, filed Dec. 3, 2001, and claims priority to CanadianApplication No. 2,327,370, filed Dec. 5, 2000, each of which are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to new particles based on Li₄Ti₅O₁₂, basedon Li_((4-α))Z_(α)Ti₅O₁₂, or based on Li₄Z_(β)Ti_((5-β))O₁₂.

The present invention also relates to processes that make it possible toprepare these particles and to their use, especially in the area ofelectrochemical devices such as electrochemical generators.

DESCRIPTION OF PRIOR ART

Marketing of the lithium-ion battery by Sony, in 1990, was reported byNaguara and Tozawa, Prog. Batt. Solar Cells, 9 (1990), 209. It madepossible an expansion and a significant breakthrough of batteries intothe area of portable devices (telephone, computer). The technology ofLi-ion batteries is based on lithium intercalation electrodes, inparticular the anode which is made of graphite. At the time of the firstcharge, a passivation film is formed on the carbon surface. Thechemistry and the composition of this passivation film are complex. Theelectrochemical formation protocol for this film remains an industrialsecret. In addition, at the time of insertion of lithium in carbon,there is a volume variation of 10%, which induces a discontinuitybetween the particles causing loosening of the interfaces between theelectrode and the electrolyte, and between the electrode and the currentcollector.

Once intercalated (LiC₆), the potential of the carbon gets closer to theone of the lithium deposit, which makes the electrode more reactive. Theprojection of the small battery to a higher scale for hybrid andelectric vehicle applications requires a large quantity of electrolyteswhich makes the safety aspect much more significant.

Titanium oxide spinel Li₄Ti₅O₁₂ is a material for anodes promising forlithium-ion batteries due to its intercalation potential (K. Zaghib etal., 190^(th) Electrochemical Society Meeting, San Antonio, Abs. no. 93,1996), cyclability, rapid charging-discharging at high current such asdescribed by K. Zaghib et al. in Proceeding on Lithium PolymerBatteries, PV96-17, p. 223) in The Electrochemical Society ProceedingSeries (1996), (K. Zaghib et al., J. Electro chem. Soc. 145, 3135,(1998) and in J. Power Sources, 81-82 (1999) 300-305). The coefficientof diffusion of lithium in Li₄T₅O₁₂ is of a higher order of magnitudethan the coefficient of diffusion of lithium in carbons (regarding thissubject, see K. Zaghib et al., J. Power Sources, 81-82 (1999) 300-305).This characteristic distinguishes Li₅Ti₅O₁₂ from the other potentialcandidates for power applications, such as PNGV and GSM pulses. Duringthe intercalation of lithium, the structure of Li₄Ti₅O₁₂ does not varyin volume, which makes this electrode very stable and thus safe. Thisstudy was carried out by Ozhuku and reported in J. Electrochem. Soc.,140, 2490 (1993) by X-ray diffraction and by scanning microscopy in situby Zayhib et al. (and reported in Proceeding on Lithium PolymerBatteries, PV96-17, p. 223 in The Electrochemical Society ProceedingSeries (1996) and in J. Electro chem. Soc. 145, 3135, (1998).

The material Li₄Ti₅O₁₂ because of its lack of volume expansion (alsocalled as zero volume expansion (ZEV)) has been easily used in polymer,ceramic or glass electrolyte batteries, which ensures good cyclingstability. In addition, the good behavior of this anode at 1.5 Vpromotes the use of any type of liquid electrode, such as ethylenecarbonate (EC), propylene carbonate (PC) or mixtures of these two. Atthis potential level, there is no passivation film formation on theelectrode, which on one hand prevents the release of gas due to theelectrolyte reduction, and on the other hand, prevents loss of capacity.This operation potential increases the life span of the battery,especially for stand-by type applications because of its character aselectrode without passivation film. The use of Li₄Ti₅O₁₂ as an anodedoes not require any prior forming of the battery.

In addition, in the configuration of the plastic metal type battery, asecondary pocket is reserved for gas due to electrolyte decompositionwhen carbon is used as the anode. The fact that the battery withLi₄Ti₅O₁₂ does not need either forming or a reserve pocket for degassingwill reduce the manufacturing cost of the battery.

The insertion reaction of Li₄Ti₅O₁₂ occurs as follows:Li₄Ti₅O₁₂+3Li⁺+3e ⁻←→Li₇Ti₅O₁₂  (1)

In the literature (T. Ohzuku, et al., J. Electrochem. Soc., 140, 2490(1993)) and (J. Schoonman et al., the 198^(th) Meeting of theElectrochemical Society Phoenix, Extend Abstract No. 91, 92 and 98,October 2000), the Li₄Ti₅O₁₂ is mentioned as being able to be obtainedby a binary mixture of a mixture of LiOH and TiO₂ where the synthesistemperature is greater than 600° C. Residual impurities of the TiO₂,Li₂TiO₃ and/or other type in the mixture limit the electrode capacityand limit the size of the particles.

In the document entitled “Solid state lithium ion batteries using carbonor an oxide as negative electrode”, J. Electrochem. Soc., Vol. 145,3135, (1998) K. Zaghib, M. Armand and M. Gauthier describe all thedifferent possible applications of Li₄Ti₅O₁₂ as anode or cathode inrechargeable batteries or supercapacitors.

In the document “Electrochemistry of anodes in solid-state Li-ionpolymer batteries” J. Electrochem. Soc., Vol. 145, No. 9, September1998, the electrochemical performance of solid-state lithium ionbatteries that are produced using an electrolyte based on solid polymersfree of solvent is described. A cell based on Li₄Ti₅O₁₂ as cathode withlithium as anode, at a rate of C/1 supplies 150 mAh/g, which correspondsto 97% of the efficiency of nominal capacity. The irreversible capacitywas high when carbon was used as the negative electrode. However, thesacrificial capacity was very slight when carbon was replaced with aspinel material.

In the document “Electrochemical study of Li ₄ Ti ₅ O ₁₂ , a negativeelectrode for li-ion polymer rechargeable batteries” K Zaghib et al.give evidence of the electrochemical stability of a negative electrodefor lithium ions containing Li₄Ti₅O₁₂ of the same type as that describedin the preceding example regarding its coefficient of chemical diffusionfor a Li₄Ti₅O₁₂ structure of the spinel type which results in acoefficient of diffusion with a value of −2.10⁻⁸ cm².s⁻¹, which gives avalue that is greater in intensity than that of the carbon negativeelectrodes. Thus the Li₄Ti₅O₁₂ electrode offers advantages forelectrochemical cells which are safety, long life span and reliability.

The U.S. Pat. No. 6,221,531 describes a structure of the spinel typewith the general formula Li[Ti_(1.67)Li_(0.33-y)M_(y)]O₄, whereinY<0≦0.33 with M representing magnesium and/or aluminum. This structureis presented as useful for making up a negative electrode for anon-aqueous electrochemical cell and in a non-aqueous battery comprisinga plurality of cells, connected electrically, each cell comprising anegative electrode, an electrolyte and a positive electrode, thenegative electrode being made up of this spinel structure.

Thus there was a need for new types of particles free of the limitationsand/or disadvantages commonly associated with particles of the prior artpreviously mentioned and, in particular, making possible the productionof high-performance electrochemical devices with cycling stability, easyto spread on a support such as an electrode and with good flexibility asregards to the thickness of the electrode that will be produced usingthese particles.

IN THE DRAWINGS

FIG. 1: illustrates the different applications of the Li₄Ti₅O₁₂particles (coated with carbon or not) as anode or as cathode forbatteries and supercapacitors.

FIG. 2: illustrates comparative performances of a process according tothe invention compared with those of a classic process such as describedin Prog. Batt. Solar Cells, 9 (1990), 209.

FIG. 3: illustrates the double role of carbon in the preparation processfor new particles and in the composition of the carbon layer that coatsthem.

FIG. 4: illustrates a classic formation process for Li₄Ti₅O₁₂(macroscopic particle), in the absence of carbon; this process makes itpossible to obtain a spinel structure in the presence of impurities of aTiO₂ or other type. This structure is limited for electrochemicalperformance, to currents less than 2 C.

FIG. 5: illustrates the same process illustrated in FIG. 4, with theexception of the reagent LiOH which is substituted by Li₂CO₃; this typeof process yields a formation of agglomerates of the Li₄Ti₅O₁₂ type.

FIG. 6: illustrates a process according to the invention for theformation of nano-particles of Li₄Ti₅O₁₂ from a ternary mixtureLiOH—C—TiO₂, intimately mixed at high energy, this mixture is heated at400° C. then to 600° C. This type of process gives rise to the formationof nano-agglomerates of Li₄T₅O₁₂.

FIG. 7: illustrates a process similar to the one shown in FIG. 6, withthe exception that LiOH is substituted by Li₂CO₃; this type of processleads to the formation of Li₄Ti₅O₁₂ nano-agglomerates.

FIG. 8: illustrates a process similar to the one illustrated in FIG. 7,by adding Li₂CO₃ to the initial product; this type of process makes itpossible to obtain Li₄Ti₅O₁₂ nano-agglomerates.

FIG. 9: illustrates a process similar to those shown in FIGS. 6 and 7,with the exception that calcination is carried out in an inertatmosphere; this type of process makes it possible to obtain Li₄Ti₅O₁₂nano-agglomerates of Li₄Ti₅O₁₂ coated with carbon. This structure givesexceptional electrochemical performance at high current density (12 C).

FIG. 10: illustrates the advantages of a pretreatment of the mixturemilled at high energy. Dry process. Homogeneous precursor. Homogeneousspecific surface area. Coating of particles with carbon. Direct contactof particle with carbon. Direct contact via carbon with the reactiveparticles. Carbon is a very good thermal conductor. Low contamination.Homogeneous dispersion. Acceleration or rapid synthesis. Obtaining amixture of nanostructures after the thermal treatment.

FIG. 11: illustrates the mechanism and the role of carbon coating, thelatter coating making it possible to obtain a large diffusion of lithiumin Li₄Ti₅O₁₂ and obtain 90% of the nominal capacity at 12 C.

FIG. 12: illustrates the mechanism of the technology of hybridsupercapacitors using an anode of the nano-Li₄Ti₅O₁₂ type.

FIG. 13: is the TGA curve of a mixture of TiO₂+Li₂CO₃+carbon aftermilling at high energy for 2 hours, in air and in argon; the reactionstarts at 400° C. (in argon and in air).

FIG. 14: is a SEM photo of microscopic particles of Li₄Ti₅O₁₂ obtainedfrom a mixture of Li₂CO₃+TiO₂.

FIG. 15: is a SEM photo of nanoscopic particles of Li₄Ti₅O₁₂ obtainedusing a mixture of Li₂CO₃+TiO₂+carbon.

FIG. 16: illustrates a manufacturing process for nanoparticles ofLi₄Ti₅O₁₂ coated with carbon and obtained by coating the particles ofTiO₂ with organic formulations of the polyol type and/or of the PE-POtype; the thermal treatment carried out in inert atmosphere transformsthe organic part into carbon. This process is carried out in the step ofmixed Jar milling with solvent or dry.

FIG. 17: illustrates a manufacturing process for nanoparticles ofLi₄Ti₅O₁₂ coated with carbon and obtained by coating the particles ofTiO₂ with inorganic formulations of the Al₂O₃, ZrO₂ type, the thermaltreatment carried out in inert atmosphere transforming the organic partto carbon. This process is carried out in the step of mixed Jar millingwith solvent or dry.

FIG. 18: illustrates a manufacturing process for nanoparticles ofLi₄Ti₍₅₋₎AlO₁₂ coated with carbon and obtained by coating the particlesof TiO₂ using a hybrid inorganic-organic formulation.

SUMMARY OF THE INVENTION

The present invention concerns a synthesis process for new particles ofthe formula Li₄Ti₅O₁₂, of the formula Li_((4-α))Z_(α)Ti₅O₁₂ or of theformula Li₄Z_(β)Ti_((5-β))O₁₂, wherein α represents a number greaterthan zero and less than or equal to 0.33, β represents a number greaterthan 0 and less than or equal to 0.5, Z represents a source of at leastone metal, preferably chosen from the group made up of Mg, Nb, Al, Zr,Ni, Co. These particles are coated with a layer of carbon. Use of theseparticles in electrochemical systems also constitutes an object of thepresent invention.

DESCRIPTION OF THE INVENTION

A first object of the present invention consists of a process that makespossible the preparation of particles comprising:

-   -   a core of Li₄Ti₅O₁₂, a core of Li_((4-α))Z_(α)Ti₅O₁₂ or a core        of Li₄Z_(β)Ti_((5-β))O₁₂, α representing a number greater than        zero and less than or equal to 0.33, β representing a number        greater than 0 and less than or equal to 0.5, Z representing a        source of at least one metal, preferably chosen from the group        made up of Mg, Nb, Al, Zr, Ni, Co; and    -   a coating of carbon.

According to an advantageous embodiment, this synthesis process makespossible the preparation of particles of Li₄Ti₅O₁₂ (preferably withspinel structure) coated with carbon, said particles comprising from0.01 to 10%, preferably 1 to 6%, and still more preferably around 2% byweight of carbon, the quantity of carbon being expressed with respect tothe total mass of Li₄Ti₅O₁₂ particles;

-   -   said process comprising the steps of        -   a) preparation of a dispersion of a ternary mixture            (preferably an intimate ternary mixture) of            TiO_(x)—Li_(z)Y-carbon, wherein            -   x represents a number between 1 and 2,            -   z represents 1 or 2, and            -   Y represents a radical chosen among CO₃, OH, O and TiO₃                or a mixture of them; and        -   b) heating of the dispersion obtained in the preceding step,    -   the operating conditions, more specifically the concentration        conditions of components of the ternary mixture submitted to        dispersion, being chosen in such a way as to yield a conversion,        preferably a complete conversion, of the initial products into        Li₄Ti₅O₁₂.

According to another advantageous embodiment, the process according tothe invention makes possible the synthesis of particles ofLi_((4-α))Z_(α)Ti₅O₁₂ (preferably with spinel structure) coated withcarbon, α representing a number greater than zero and less than or equalto 0.33, Z representing a source of at least one metal, preferablychosen from the group made up of Mg, Nb, Al, Zr, Ni, Co, said particlescomprising from 0.01 to 10%, preferably 1 to 6%, and still morepreferably around 2% by weight of carbon, the quantity of carbon beingexpressed with respect to the total mass of Li_((4-α))Z_(α)Ti₅O₁₂particles;

-   -   said process comprising the steps of        -   a) preparation of a dispersion of an intimate ternary            mixture of TiO_(x)LiY-carbon, wherein            -   x represents a number between 1 and 2,            -   z represents 1 or 2, and            -   Y represents a radical chosen among CO₃, OH, O and TiO₃                or a mixture of them; and        -   b) heating of the dispersion obtained in the preceding step,            preferably at a temperature comprised between 400 and 1,000°            C.,            the operating conditions, more specifically the            concentration conditions of components of the ternary            mixture submitted to dispersion, being chosen in such a way            as to yield a conversion, preferably a complete conversion,            of the initial products into Li_((4-α))Z_(α)Ti₅O₁₂, and            the source of at least one metal Z being added to the            reaction mixture, preferably in step a) of said process in a            content that is preferably from 0.1 to 2% by weight,            expressed with respect to the mass of said ternary mixture.

Operating conditions that make possible the specific preparation ofparticles of the formula Li_((4-α))Ti₅O₁₂ are, more specifically, acontrol of the initial quantities of each of the compounds present inthe ternary mixture that is used for preparation of the dispersion.

According to another embodiment, the process of the invention makespossible the synthesis of particles of the formula Li₄Z_(β)Ti_((5-β))O₁₂(preferably with spinel structure), wherein β is greater than 0 and lessthan or equal to 0.5, coated with carbon, Z representing a source of atleast one metal, preferably chosen from the group made up of Mg, Nb, Al,Zr, Ni, Co, said particles comprising from 0.01 to 10%, preferably 1 to6%, and still more preferably around 2% by weight of carbon, thequantity of carbon being expressed with respect to the total mass ofLi₄Z_(β)Ti_((5-β))O₁₂ particles;

-   -   said process comprising the steps of        -   a) preparation of a dispersion of an intimate ternary            mixture of TiO_(x)—LiY-carbon, wherein            -   x represents a number between 1 and 2,            -   z represents 1 or 2, and            -   Y represents a radical chosen among CO₃, OH, O AND TiO₃                or a mixture of them; and        -   b) heating of the dispersion obtained in the preceding step,            preferably to a temperature comprised between 400 and 1,000°            C.,            the operating conditions, more specifically the            concentration conditions of components of the ternary            mixture submitted to dispersion, being chosen in such a way            as to yield a conversion, preferably a complete conversion,            of the initial products into Li₄Z_(β)Ti_((5-β))O₂, and the            source of at least one metal Z being added to the reaction            mixture, preferably in step a) of said process in a content            that is preferably from 0.1 to 2% by weight, expressed with            respect to the mass of said ternary mixture,            the operating conditions that make possible the specific            preparation of particles of the formula            Li₄Z_(β)Ti_((5-β))O₁₂ are, more specifically, a control of            the initial quantities of each of the constituents present            in the ternary mixture that is used for preparation of the            dispersion.

According to an advantageous embodiment of the process, the dispersionof the ternary mixture is heated at a temperature of around 600° C.

Still more advantageously, the dispersion is heated in two steps, thefirst step being carried out until the dispersion reaches a temperatureof about 400° C., the second step being carried out at approximately600° C.

The first step is preferably carried out by rapid heating at around 400°C., preferably during a period of 1 to 4 hours.

The second step is carried out by slow heating, preferably for at leastfour hours.

According to another advantageous embodiment of the process, at leastone step, which is preferably step a), is carried out in air.

According to another advantageous embodiment of the process, at leastone step, which is preferably step b), is carried out at least partiallyin inert atmosphere.

The dispersion of the ternary mixture is advantageously prepared usingwater and/or at least one solvent that is preferably an organic solvent.This organic solvent is advantageously chosen from the group made up ofketones, saturated hydrocarbons, unsaturated hydrocarbons, alcohols andmixtures of them, still more preferably the dispersion of the ternarymixture is prepared using water, acetone, heptane, toluene or using amixture of them.

Said dispersion is also prepared dry, without solvent.

According to another preferred embodiment, a compound Li_(z)Y, whichcomprises at least one compound chosen from the group made up of Li₂O,Li₂CO₃ and LiOH, is chosen. Still more preferably, the Li_(z)Y compoundcomprises exclusively Li₂CO₃, said Li₂CO₃ preferably being present in aratio of 25 to 30% by weight with respect to the total mass of theternary mixture.

Advantageously, the dispersion is carried out by mechanical milling,preferably by high-energy mechanical milling, preferably dry and/or byJar milling, preferably with a solvent.

According to another preferred embodiment, a TiO_(x) compound of theanatase or rutile TiO₂ type (preferably the anatase TiO₂ type), or amixture of both, is chosen and TiO₂ is preferably present in saidternary mixture in concentrations of 58 to 71% by weight.

The compound Li_(z)Y preferably comprises Li₂TiO₃, this Li₂TiO₃preferably being present in a quantity of 43 to 48% by weight of Li₂TiO₃with respect to the total mass of the ternary mixture.

The carbon used to carry out the process according to the invention maycome from any source. Advantageously, the carbon is chosen from thegroup made up of natural or artificial graphite, carbon black(preferably acetylene black), Shawinigan black, Ketjen black and cokes(preferably petroleum coke) and is added to the reaction mixture,preferably at the beginning of the preparation of the dispersion of theternary mixture.

The carbon can also be produced in the course of said process,preferably from at least one free organic material, such as a polymer,present in the reaction mixture.

The carbon can also be produced at the surface of the particles bycalcination of an organic and/or inorganic material deposited, in thecourse of said process, on the surface of the Li₄Ti₅O₁₂ particles and/oron the surface of the particles based on Li₄Ti₅O₁₂ and/or on the surfaceof at least one of the reagents used (preferably the TiO₂) for thepreparation of the dispersion of said ternary mixture.

Preferably, the carbon used is in the form of particles having aspecific surface area greater than or equal to 2 m²/g, preferably in theform of particles having a specific surface area greater than or equalto 50 m²/g.

According to an advantageous embodiment, the process of the invention iscarried out in the presence of an atmosphere containing oxygen, a partof the carbon present in the reaction mixture then being consumed duringsaid process.

According to another advantageous embodiment, the coating of carbon isobtained from the presence, in the reaction mixture, of a powder ofShawinigan carbon and/or at least one polymer, which is preferably apolyol or a polyethylene-polyoxide ethylene copolymer.

According to another advantageous embodiment, as an initial product TiO₂that is coated with at least one inorganic material, with an inorganicmaterial that preferably comprises an aluminum oxide and/or a zirconiumoxide and still more preferably at least one organic material thatcomprises Al₂O₃ and/or ZrO₂, is used. According to another variation,TiO₂ that is coated with a hybrid inorganic-organic material is used.

A second object of the present invention is made up of particles thatcan be obtained by use of one of the processes previously defined forthe first object of the invention.

These particles comprise a core coated with carbon, the core of saidparticles being:

-   -   based on Li₄Ti₅O₁₂; or    -   based on Li_((4-α))Z_(α)Ti₅O₁₂, wherein α is greater than zero        and less than or equal to 0.33, Z representing a source of at        least one metal, preferably chosen from the group made up of Mg,        Nb, Al, Zr, Ni, Co; or    -   based on at least one compound of the formula        Li₄Z_(β)Ti_((5-β))O₁₂ with β greater than 0 and/or less than or        equal to 0.5, Z representing a source of at least one metal,        preferably chosen from the group made up of Mg, Nb, Al, Zr, Ni,        Co.

A preferred sub-family is made up of particles wherein the core mainlycomprises preferably at least 65% of Li₄Ti₅O₁₂, of Li_((4-α))Z_(α)Ti₅O₁₂or Li₄Z_(β)Ti_((5-β))O₁₂ or a mixture of these.

The complement notably being made up of TiO₂ Li₂TiO₃ or the residues ofsolvents.

Still more advantageously, the core of the particles according to theinvention is exclusively made up of Li₄Ti₅O₁₂, of Li_((4-α))Z_(α)Ti₅O₁₂or Li₄Z_(β)Ti_((5-β))O₁₂ or a mixture of these.

A preferred sub-family of particles of the present invention is made upof particles that have a reversible capacity, measured according to themethod defined in the description, which is between 155 and 170 mAh/g.

According to an advantageous method, these particles are made up of acore of Li₄Ti₅O₁₂ coated with a layer of carbon.

The particles according to the invention are preferably nanostructures.Their size, measured with scanning electron microscopy, is preferablycomprised between 10 and 950 nanometers.

The particles according to the present invention are also characterizedby their core, which has a size measured using scanning electronmicroscopy that is preferably comprised between 10 and 500 nanometers.

The carbon coating that covers these particles is characterized by athickness that, also measured using scanning electron microscopy, iscomprised between 10 and 450 nanometers, still more preferably thethickness of the coating varies between 20 and 300 nanometers.

A third object of the present invention is made up of a cathode of anelectrochemical generator (preferably a recyclable type electrochemicalgenerator) comprising particles such as previously defined in the secondobject of the present invention and/or such that can be obtained byusing any one of the processes according to the first object of thepresent invention.

A fourth object of the present invention is made up of an anode for anelectrochemical generator (preferably a recyclable type electrochemicalgenerator) comprising particles such as previously defined in the secondobject of the present invention and/or such that can be obtained byusing any one of the processes according to the first object of thepresent invention.

A fifth object of the present invention is made up of an electrochemicalgenerator (preferably of the rechargeable type) of the lithium typecomprising an anode of the metallic lithium type and a cathode of theLi₄Ti₅O₁₂ type and/or of the Li_((4-α))Z_(α)Ti₅O₁₂ type and/or of theLi₄Z_(β)Ti_((5-β))O₁₂ type or mixtures of them, the cathode in thisbattery being such as previously defined in the third object of thepresent invention.

A sixth object of the present invention is made up of an electrochemicalgenerator (preferably of the rechargeable type) of the lithium-ion typecomprising an anode of the Li₄Ti₅O₁₂ type and/or theLi_((4-α))Z_(α)Ti₅O₁₂ type and/or the Li₄Z_(β)Ti_((5-β))O₁₂ type ormixtures of them and a cathode of the LiFePO₄, LiCoO₂, LiCoPO₄, LiMn₂O₄and/or LiNiO₂ type or mixtures of them wherein the anode is such asdefined in the third object of the present invention.

Preferably, such a generator uses, in the anode and/or in the cathode, acurrent collector of solid aluminum or of the Exmet type (expandedmetal).

A preferred sub-family of the electrochemical generators according tothe present invention is made up of generators that do not require anyprior forming of the battery.

A seventh object of the present invention is made up of a hybrid-typesupercapacitor comprising an anode of the Li₄Ti₅O₁₂ type and/or theLi_((4-α))Z_(α)Ti₅O₁₂ type and/or the Li₄Z_(β)Ti_((5-β))O₂ type and acathode of the graphite or carbon type with a large specific surfacearea, wherein the anode is as defined previously, not requiring anypreliminary forming of the supercapacitor.

According to an advantageous embodiment, the anode and/or the cathode ofsuch a supercapacitor is (are) equipped with a current collector ofsolid aluminum or of the Exmet (expanded metal) type.

According to a preferred embodiment, the electrolyte used in theelectrochemical generator or in the supercapacitor is dry polymer, gel,liquid or ceramic in nature.

The Invention is More Specifically Carried Out According to One of theOperating Methods Explained Below:

1—In the Presence of Carbon Powder

The present invention makes available a new synthesis method forLi₄Ti₅O₁₂ that is simple, fast and less costly. The synthesis is basedon a ternary mixture of TiO₂ with anatase or rutile structure, of Li₂CO₃and carbon. The mixture is well dispersed, then submitted to a heatingphase that comprises two steps. The first step is rapid heating to 400°C. in air. This temperature stage helps, on one hand, to eliminate thetraces of heptane when this solvent is used and, on the other hand, tostimulate the release of CO₂. The second step to 600° C. is longer andrequires a minimum of 4 hours. This completes the transformation of theternary mixture to Li₄Ti₅O₁₂ with spinel structure. The fineness of theparticle size is obtained due to a longer heating time during the secondstep (see the illustration given in FIG. 2).

Carbon plays a crucial role in the synthesis (for this subject, see FIG.3). In the first place, the carbon is oxidized with the oxygen in theair, with oxygen coming from TiO₂ while releasing CO₂. In the secondplace, titanium reacts with lithium, forming lithiated titanium. Thelatter oxidizes with air. The synthesis reaction can be schematicallyillustrated as follows:5TiO₂+XC+2Li₂CO₃→Li₄Ti₅O₁₂+(X+2)CO₂  (2)

An excess of carbon is used to ensure complete transformation. In fact,carbon burns in the presence of air, then its excess reduces TiO₂ andLi₂CO₃. In this invention, carbons that contain oxygen groups at thesurface are used. The latter react with the lithium oxide. TheTiO₂-carbon-Li₂CO₃ mixture can be produced using two methods: in asolvent or in a dry mixture dispersed mechanically. Once the intimatehomogeneous powder is obtained, the carbon will play the essential roleestablished according to reaction (2) by obtaining a Li₄Ti₅O₁₂ productwithout impurities.

The use of Li₂O instead of Li₂CO₃ works well, however with the leasttrace of humidity there will be formation of LiOH, which reduces theLi₄Ti₅O₁₂ production yield and makes it necessary to maintain thesynthesis at 800° C.

The synthesis was also carried out with the TiO₂—Li₂CO₃-carbon mixturedispersed by high-energy mechanical milling (HEMM). The main step beforethe passage to HEMM is to disperse the ternary mixture well in order toobtain a homogeneous mixture (FIG. 10). For this, first a co-milling for15 minutes to 2 hours is used, in addition, this co-milling also helpsto lower the synthesis temperature. This process produces particles onthe nanostructure scale of Li₄Ti₅O₁₂ (FIGS. 6, 7 and 8), compared to theclassic method that makes it possible to carry out the formation of themacroscopic particles (FIGS. 4 and 5). The use of these nanostructureparticles makes it easier to spread thin electrodes and increases thediffusion of lithium in the spinel structure for power applications. TheLi₄Ti₅O₁₂ applications are presented in FIG. 1. In the case whereLi₄Ti₅O₁₂ is a cathode, the battery produces 1.5 volts, due to therechargeability of the Li₄Ti₅O₁₂, this system becomes very interestingfor the rechargeable battery markets, thus replacing the large market ofprimary alkaline batteries of 1.5 volt.

Li₄Ti₅O₁₂ is a white insulating powder, in order to increase itselectronic conductivity, it is co-milled with carbon. The latter coatsthe particles of Li₄Ti₅O₁₂ and gives a good conductivity to theelectrode at the time of intercalation and disintercalation of lithiumand keeps its capacity (mAh/g) stable at elevated currents (mA/g). Infact, carbon plays a double role in this invention, on one hand, ithelps to synthesize a final pure product of the Li₄Ti₅O₁₂ type bylowering the synthesis temperature, and on the other, it increases theelectronic conductivity by co-milling with Li₄Ti₅O₁₂ for manufacturingelectrodes for an electrochemical generator.

2—In the Presence of Organic Coating on the Surface of the TiO₂Particles

The synthesis of the TiO₂ mixture coated with organic material (producedby the Kronos company) with Li₂CO₃. The two components are diluted inwater. The intimate mixture is obtained by Jar milling for 24 hours. Thepaste obtained is dried at 120° C. during 12 hours. The mixture isdispersed by “vapour jet milling from the Kronos company.” A two stagethermal treatment, 400 and 850° C. in inert atmosphere, yields particlesof nano-Li₄Ti₅O₁₂ coated with carbon (FIG. 16).

3. In the Presence of Free Organic Material in the Mixture

The synthesis of the mixture of standard TiO₂ and an organic material(polyol, PE-PO or other) with Li₂CO₃ or LiOH (or mixtures of them. Thethree components are diluted in water. The intimate mixture is obtainedby Jar milling over 24 hours. The paste obtained is dried at 120° C.during 12 hours. The mixture is dispersed by “vapour jet milling fromthe Kronos company.” A two stage thermal treatment, 400 and 850° C. ininert atmosphere, yields nano-particles of Li₄Ti₅O₁₂ coated with carbon.

4. In the Presence of Inorganic Coating on the Surface of TiO₂ Particles

The synthesis of the mixture of TiO₂ coated with an inorganic materialof the type Al₂O₃, ZrO₂ and the like (product from the Kronos company)with Li₂CO₃ or LiOH (or a mixture of them). The two components, mixedwith the organic material are diluted in water. The intimate mixture isobtained by Jar milling during 24 hours. The paste obtained is dried at120° C. during 12 hours. The mixture is dispersed by “vapour jet millingfrom the Kronos company.” A two stage thermal treatment, 400 and 850° C.in inert atmosphere, yields particles of Li_((4-α))Z_(α)Ti₅O₁₂ or ofLi₄Z_(β)Ti_((5-β))O₁₂ coated with carbon (FIG. 17).

5. In the Presence of Hybrid Organic-Inorganic Coating on the Surface ofTiO₂ Particles

The synthesis of the mixture of TiO₂ coated with hybridorganic-inorganic material of the polyol type, preferably a high puritypolyol, still more preferably trimethylpropane or an ethylenepolyethylene-polyoxide copolymer, Al₂O₃, ZrO₂ or the like (product fromthe Kronos company) with Li₂CO₃ or LiOH (or a mixture of them). The twocomponents are diluted in water. The intimate mixture is obtained by Jarmilling for 24 hours. The paste obtained is dried at 120° C. for 12hours. The mixture is dispersed by vapour jet milling from the Kronoscompany. Thermal treatment at two stages, of 400 and 850° C. in inertatmosphere, yields nano-particles of Li_((4-α))Z_(α)Ti₅O₁₂ or ofLi₄Z_(β)Ti_((5-β))O₁₂ coated with carbon (FIG. 18).

6. Use of Nano-Li₄Ti₅O₁₂ Coated with Carbon as an Anode in HybridSupercapacitor Technology (HSC)

This technology (FIG. 12) uses an insertion anode of the Li₄Ti₅O₁₂ typeplaced face to face with a cathode of the graphite or carbon type withlarge specific surface area (double layer) with a polymer, gel, liquidor ceramic electrolyte. The advantage of nano-Li₄Ti₅O₁₂ coated withcarbon (FIG. 11) promotes the diffusion of lithium inside the spinelstructure, and in particular, at elevated currents like 12 C(charge-discharge in 5 minutes). At these ratings, the HSC develops 90%of the nominal capacity. The presence of carbon provides goodconductivity at the grain level and on the scale of the electrode, whichlimits the addition of large proportions of carbon to the electrode.This makes it possible to increase the energy density of the HSC.

HSC technology uses two collectors of the Exmet (expanded metal) type inaluminum with an electrolyte having a salt mixture of LiTFSI+LiBF₄ orLiTFSI+LiPF₆ or LiTFSI+BETi+LiBF₄. This mixture makes it possible tohave good ionic conductivity and reduces the collector corrosion duringhigh-voltage charging. The energy density of the HSC is around 60 Wh/kgand the capacity obtained is 90% at charging rates of 12 C. HSCtechnology presents an energy density comparable to Pb-acid or Ni—Cdtechnologies, in addition this technology has a long cyclability.

It is important to keep in mind that Li-ion technology (graphite/LiCoO₂)is limited to currents less than 2 C (30 minutes) and by the number ofcycles which is 1200.

EXAMPLES

The following examples are given purely as an illustration and shouldnot be interpreted as constituting any limitation whatsoever of theinvention.

Example 1 Preparation in the Presence of Heptane of Particles ofLi₄T₅O₁₂ Coated with Carbon

23 g of TiO₂ with anatase structure (commercialized by the KronossCompany, Varennes, Canada under the name XP-406) are mixed with 10 gramsof Li₂CO₃ (Aldrich, Canada) and with 20 grams of Shawinigan black. Anexcess of carbon black is used to ensure complete transformation of theCO₂ and lower the synthesis temperature.

This ternary mixture is placed in a steel container and heptane is addedin a powder/liquid ratio of around 35 g/150 ml. The heptane is used toreduce the heat and the friction between the particles of powder and theballs and leaves the product inert. Stainless steel balls are added tohomogenize the ternary mixture. After 2 hours of intimate co-milling, apowder with fine particle size is obtained. The success of theco-milling depends on lowering the synthesis temperature. The heating ofthis co-milled mixture is carried out in two steps. The first step is arapid heating to 400° C. in air. This temperature stage promotes theelimination of traces of heptane and stimulates the start of CO₂release. It was proven by the loss of weight shown by TGA (Perkinthermal analysis), which is shown in FIG. 13. The second stage consistsof slow heating to 600° C. This completes the transformation of theproduct into Li₄Ti₅O₁₂ with spinel structure. The X-ray spectrum revealsthe presence of peaks characteristic of the Li₄Ti₅O₁₂ structure.

Example 2 Dry Preparation of Particles of Li₄Ti₅O₁₂ Coated with Carbon

23 g of TiO₂ with anatase structure (XP-406 from the Kronos Company,Varennes) are mixed with 10 grams of Li₂CO₃ (Aldrich, Canada) and with20 g of Shawinigan black. Again an excess of carbon black is used toensure complete transformation of the CO₂ and lower the synthesistemperature. This ternary mixture is placed in a dry container withstainless steel balls.

After 2 hours of intimate milling, a powder with a fine particle size isobtained. Heating of this co-milled mixture is carried out in two steps,at 400° C. and then at 600° C. The X-ray spectrum reveals the presenceof a spinel structure for the Li₄Ti₅O₁₂ particles thus synthesized.

Example 3 Dry Preparation and Characterization of Nano-Particles ofLi₄T₅O₁₂ Coated with Carbon

23 g of TiO₂ with anatase structure (XP-406 from the Kronos Company,Varennes) are mixed with 10 grams of Li₂CO₃ (Aldrich, Canada) and with 2grams of Shawinigan black. A 6-gram excess of carbon black is again usedto ensure complete transformation of the CO₂ and to lower the synthesistemperature. This ternary mixture is subject to high-energy mechanicalmilling (using a shaker mill machine of the type SPEX 8000) in thepresence of stainless steel balls in a ball:powder ratio of 10:1. Themilling period can vary between 3 minutes and 3 hours, which in the caseof the present example is 2 hours. Heating of the co-milled mixture iscarried out in two steps. The first step consists of rapid heating to400° C. in air. The second step consists of slow heating to 600° C. Thiscompletes the transformation of the product into Li₄Ti₅O₁₂ with spinelstructure. The X-ray spectrum confirms the presence of peakcharacteristics of the spinel structure of the Li₄Ti₅O₁₂.

FIG. 15, which is a photograph obtained using scanning electronmicroscopy, shows that the particles of Li₄Ti₅O₁₂ are of nanoscopicsize. FIG. 14 relates to a photo obtained in the same manner, but forparticles prepared without the addition of carbon shows that thecorresponding particles are of macroscopic size.

Example 4 Preparation and Evaluation of an Electrode ContainingParticles of Li₄Ti₅O₁₂ Coated with Carbon

According to the synthesis process used in example 1, the particles ofLi₄Ti₅O₁₂, of poly(vinylidene fluoride) (PVDF) and Ketjen black, presentin a mass ratio of 87/10/3 are mixed. This mixture is applied to anexmet electrode of aluminum, then heated for 12 hours with nitrogenscavenging. The electrode thus prepared is then heated for 2 hours invacuum.

The electrode is then assembled in an electrochemical cell of around 4cm² with a Celgard type separator facing the lithium metal. The solventis of the TESA type (tetra ethyl sulfone amine) ethylene carbonate typewith LiTFSI salt (lithium trifluoromethanesulfonimide). The cycling iscarried out, at ambient temperature, between 1.2 and 2.5 V. Thereversible capacity obtained is 155 mAh/g with an average voltage of1.55 V.

Example 5 Providing Evidence of the Importance of Good Homogenization ofthe Ternary Mixture

According to the synthesis process described in example 1 above,Li₄Ti₅O₁₂ and Ketjen black, in a volume ratio 40/3, are co-milled inheptane in the presence of stainless steel balls. The mixture is dried,then mixed with a polymer solution based on a polyether marketed by theBaker Hughes Company, USA under the commercial name UNITHOX 750, in avolume ratio 43/57. This mixture is then applied to an aluminumcollector, then heated for 12 hours with nitrogen scavenging. Thecollector thus processed is then heated for 2 hours in vacuum.

The electrode is assembled in an electrochemical cell with about 4 cm²surface area with a separator of the polymer type based on saltcontaining polyether prepared in a laboratory, with LiTFSI salt (tetrafluoro sulfur lithium imide) placed face to face with the lithium metalas anode. Cycling is carried out at 80° C. between 1.2 and 2.5 V. Thereversible capacity obtained is 155 mAh/g in C/24 and it is 96% of thenominal capacity obtained with a rapid rating in C/1. The cell thusprepared demonstrates good cycling stability, more than 1500 cycles inC/1.

The use of co-milling and carrying out of a good intimate dispersionbetween the Li₄Ti₅O₁₂ oxide and the carbon black ensures thereproducibility of the results.

On the other hand, if the Li₄Ti₅O₁₂ oxide is mixed without co-millingwith the carbon black and the polymer, in a volume ratio 40/3/57 and ifthis mixture is applied to an aluminum collector, then heated for 12hours with nitrogen scavenging and then heated for 2 hours in a vacuum,the electrochemical result obtained by introduction of this electrode ina cell without solvent (completely solid) comprising a polymer(polyether) at 80° C. is 150 mAh/g in C/24 while only 75% of the nominalvalue is found with fast loading in C/1. In fact, this is due to thepoor dispersion between the oxide and the carbon black. In addition, thereproducibility of the results is uncertain.

Example 6 Preparation of Li₄Ti₅O₁₂ Using a Binary Mixture of LiOH—TiO₂

In this example, particles of Li₄Ti₅O₁₂ were prepared using a binarymixture of LiOH—TiO₂ (anatase) of 10.5 and 16 g, respectively, heatedfor 18 hours in air. The X-ray spectrum obtained for these particlesestablishes the presence of peak characteristics of the spinel structureof Li₄Ti₅O₁₂ as well as the presence of traces of TiO₂ (rutile) andLi₂TiO₃.

The Li₄Ti₅O₁₂ powder obtained is mixed with PVDF and with Shawiniganblack in a weight ratio 87/10/3. This mixture, which makes up theelectrode, is applied to an aluminium Exmet support, then heated for 12hours with nitrogen scavenging. The electrode thus obtained is thenheated for 2 hours in vacuum. Said electrode is assembled in anelectrochemical cell about 4 cm² with a Celgard type separator placedface to face with lithium metal as anode. The solvent used is of theTESA type (tetra ethylsulfamide)-ethylene carbonate (1:1 by volume) with1 mol of LiTFSI (bis(trifluoromethane sulfonimide)).

The reversible capacity obtained in this case is 140 mAh/g. The capacityobtained by the binary type synthesis is thus appreciably less than thatobtained by the using ternary synthesis in the presence of carbon.

Example 7 Preparation of Li₄Ti₅O₁₂ Particles Coated with Carbon withPVDF and Shawinigan Black

According to the synthesis of example 1, Li₄Ti₅O₁₂ particles are mixedwith PVDF and Shawinigan black in a weight ratio 87/10/3. This mixtureis applied on an aluminium Exmet type electrode, then heated for 12hours with nitrogen scanning. All of this is then heated for 2 hours invacuum.

Cobalt oxide LiCoO₂ is mixed with PVDF and Shawinigan black in a weightratio 87/10/3. Then the mixture thus obtained is applied to an aluminumExmet type electrode, the assembly thus obtained is then heated for 12hours with nitrogen scanning, then in a second step is heated for 2hours in vacuum.

The Li₄Ti₅O₁₂ electrode is assembled in a lithium-ion battery face toface with the LiCoO₂ electrode as cathode with a Celgard type separator.The solvent used is of the ethylene carbonate-methyl ethylene carbonatetype (1:1 by volume) with 1 mole of lithium bis(trifluoromethanesulfonimide).

The battery voltage tends toward zero volts (33 mV). The battery iscycled between 1.2 V and 2.8 V. The average voltage is around 2.5 V. Theirreversible capacity of the first cycle is around 2%. Thisirreversibility is minimum compared to the conventional carbon/LiCoO₂system. Because of the fact that the two electrodes of theLi₄Ti₅O₁₂/LiCoO₂ system have no passivation film, the reversiblecapacity of the battery is stable for more than 500 cycles. Knowing that2.5 V yields 70% of the average voltage of the lithium-ion system of thecarbon/LiCoO₂ type, a 30% deficit remains to be recaptured. The lack ofenergy to be obtained from the carbon/LiCoO₂ system can be filled by:

-   -   an Exmet type collector based on aluminum on the anode that        makes it possible to reduce the weight of the battery        (conventional carbon/LiCoO₂ system using copper as current        collector for the anode);    -   decrease in the quantity of LiCoO₂ (absence of irreversibility)        while in the classic system, the carbon type anode consumes an        irreversible capacity of around 20% to form the passivation        film;    -   increase in the energy of the Li₄Ti₅O₁₂ system by using olivine        phosphate of the LiCoPO₄ type at high voltage or lithium        manganese with high voltage in the cathode;    -   use of a thin separator of 10 to 15 microns; and    -   simplified thin packaging of the plastic metal type.

Example 8 Preparation of an Electrochemical Cell Using a TESA TypeSolvent

According to the operating method used in example 1, Li₄Ti₅O₁₂ is mixedwith PVDF and Shawinigan black in a weight 87/10/3. This mixture isapplied to an aluminium Exmet type electrode.

The assembly thus obtained is heated for 12 hours with nitrogenscavenging, then for 2 hours.

Natural graphite NG7 (Kansai Coke, Japan) is mixed with PVDF in a weightratio 90/10. This mixture is applied to an aluminium Exmet typeelectrode. The assembly thus obtained is heated for 12 hours withnitrogen scavenging, then heated 2 hours in vacuum.

The Li₄Ti₅O₁₂ electrode is mounted face to face with the graphiteelectrode separated by a Celgard. The solvent used is PC+EC+TESA (1:1:1by volume) containing 1 mol of LiPF₅+LiTFSI.

In this example, the graphite electrode is used as cathode and theintercalation reaction is an electrolytic reaction of the double layer,of which the anion PF₆ is absorbed at the surface of the graphite. Thevoltage cycling limits are between 1.5 V and 3.0 V, for an averagevoltage of 2.25 V. This average voltage value increases the energydensity by 50% with respect to values obtained with a conventionalcarbon-carbon system.

The efficiency of the first cycle is 96%. After 200 cycles, no loss ofcapacity was observed.

Example 9 Preparation of Li₄Ti₅O₁₂ Particles Coated with Carbon Using aPolyol as a Carbon Source

87 g of particles of TiO₂ with anatase structure coated with polyol(type XP-413 from the Kronos Company in Varennes) are mixed with 35.4 gof Li₂CO₃ (Limetech, Canada). The mixture of these two compounds iscarried out in the presence of water using Jar milling. Themixture-zircon balls-free volume ratio is 1/3-1/3-1/3. Milling time is24 h. The paste obtained is dried at 120° C. for 12 hours. Calcinationof the powder obtained is carried out in a rotary kiln (fabricatedin-house) in two temperature stages. The first stage is at 400° C. forone hour and the second stage at 850° C. for 3 hours in a controllednitrogen atmosphere. The analysis by X-ray diffraction of the powdersynthesized clearly shows that nano-particles of Li₄Ti₅O₁₂ with spinelstructure are obtained (as established using SEM). The analysis ofcarbon content carried out by the carbon sulfur detector method (modelCS444, Leco, USA) clearly shows that a quantity of 2% by weight remainsin the Li₄Ti₅O₁₂ structure.

Example 10 Preparation of Li₄Ti₅O₁₂ Particles Using Polyethylene Glycolas a Source of Carbon

87 grams of TiO₂ with anatase structure (XP-406 from the Kronos Company,Varennes) are mixed with 35.4 g of Li₂CO₃ (Limetech, Canada) and with 8grams of PE-PO. The three compounds are mixed in the presence of waterusing Jar milling. The mixture-zircon balls-free volume ratios are1/3-1/3-1/3. The milling time is 24 hours. The paste obtained is driedat 120° C. for 12 hours. Calcination of the powder obtained is carriedout in a rotary kiln (fabricated in-house) in two temperature stages.The first is at 400° C. for one hour and the second at 850° C. for 3hours in a controlled nitrogen atmosphere. Analysis by X-ray diffractionof the synthesized powder clearly shows that a spinel structure withnano-particles of Li₄Ti₅O₁₂ is obtained, the size of the particles isestablished using SEM. Analysis of carbon content obtained is carriedout using the carbon sulfur detector method (model CS444, Leco, USA). Itclearly shows that 2% by weight of carbon remains present in theLi₄Ti₅O₁₂ structure.

Example 11 Preparation of Particles of Li₄Ti₅O₁₂ Coated with Carbon byCalcination and Using Coated TiO₂ Particles

87 grams of TiO₂ particles with anatase structure coated with Al₂O₃(type XP-414 from the Kronos Company, Varennes) are mixed with 35.4grams of Li₂CO₃ (Limetech, Canada) and with 7 grams of Shawinigan black.The three compounds are mixed in the presence of water using Jarmilling. The mixture-zircon balls-free volume ratios are 1/3-1/3-1/3.The milling time is 24 hours. The paste obtained is dried at 120° C. for12 hours. Calcination of the powder obtained is carried out in a rotaryoven (fabricated in-house) in two temperature stages. The first stage isat 400° C. for one hour and the second stage is at 850° C. for 3 hoursin a controlled nitrogen atmosphere. Analysis by X-ray diffraction ofthe synthesized powder clearly shows that a spinel structure withnano-particles of Li₄Ti₅O₁₂ is obtained, the size of the particles ismeasured using SEM. Analysis of the carbon content obtained is carriedout using the carbon sulfur detector method (model CS444, Leco, USA). Itclearly shows that 1.95% by weight of carbon remains present in theLi₄Ti₅O₁₂ structure.

Example 12 Preparation of Li₄Ti₅O₁₂ Particles from Particles of TiO₂Coated with an Al₂O₃-Polyls Mixture

87 grams of TiO₂ with anatase structure coated with an Al₂O₃-polyolsmixture (of XP-415 type from the Kronos Company, Varennes) are mixedwith 35.4 g of Li₂CO₃ (Limetech, Canada) and with 7 grams of Shawiniganblack. The three compounds are mixed in the presence of water using Jarmilling. The mixture-zircon balls-free volume ratios are 1/3-1/3-1/3.The milling time is 24 hours. The paste obtained is dried at 120° C. for12 hours. Calcination of the powder obtained is carried out in a rotaryoven (fabricated in-house) in two temperature stages. The first is at400° C. for one hour and the second at 850° C. for 3 hours in acontrolled nitrogen atmosphere. Analysis by X-ray diffraction of thesynthesized powder clearly shows that a spinel structure withnano-particles of Li₄Ti₅O₁₂ is obtained; the size of the particles ismeasured using SEM. Analysis of the carbon content obtained is carriedout using the carbon sulfur detector method (model CS444, Leco, USA). Itclearly shows that 1.95% by weight of carbon remains present in theLi₄Ti₅O₁₂ powder.

Example 13 Preparation of a Battery with Li₄Ti₅O₁₂ Particles Coated withCarbon and with EC+PC+DMC as Solvent

According to the operating method of example 1, Li₄Ti₅O₁₂ is mixed withPVDF and Shawinigan black in a weight ratio 87/10/3. This mixture isapplied to an aluminium Exmet electrode. All of this is heated for 12hours with nitrogen scavenging, then for 2 hours in vacuum.

Carbon with a large specific surface area (PICA, FRANCE) is mixed withPVDF in a weight ratio of 20/80. This mixture is applied to an aluminiumExmet type electrode. All of this is heated for 12 hours with nitrogenscavenging then heated for 2 hours in vacuum.

The Li₄Ti₅O₁₂ electrode is mounted face to face with a carbon electrodeas cathode, separated by a Celgard. The solvent used is EC+PC+DMC (1:1:1by volume) containing 1 mole of LiTFSI+LiBF₄.

In this example, the carbon electrode is used as cathode. Theintercalation reaction in this case is a double layer electrolyticreaction, wherein the PF6 and TFSI anions are absorbed at the carbonsurface. The cycling voltage limits are between 1.5 V and 3.0 V with anaverage potential of 2.25 V. This average voltage value increases theenergy density by 50% comparatively to the conventional carbon-carbonsystem.

The efficiency of the first cycle is 96%. After 200 cycles, no capacityloss has been observed.

Example 14 Preparation of a Battery from Particles of Li₄Ti₅O₁₂ Coatedwith Carbon

According to the operating method of example 1, Li₄Ti₅O₁₂ is mixed withPVDF and Shawinigan black in a weight ratio 87/10/3. This mixture isapplied to an aluminium Exmet electrode. All of this is heated for 12hours with nitrogen scavenging at a temperature of 120° C., then for 2hours in vacuum at a temperature of 120° C.

A conductive polymer of the polyaniline type is mixed with PVDF andShawinigan black in a weight ratio 87:10:3. The mixture thus obtained isapplied to an aluminium Exmet electrode, then heated for 12 hours withnitrogen scavenging at a temperature of 120° C., then for 2 hours invacuum at a temperature of 120° C.

The Li₄Ti₅O₁₂ electrode is mounted face to face with the carbonelectrode as cathode separated by a Celgard. The solvent used isEC+PC+DMC (1:1:1 by volume), commonly called, containing 1 mole ofLiTFSI+LiBF₄.

In this example, the polymer electrode conductor is used as cathode. Theintercalation reaction is then a doping reaction of the PF₆ and TFSIanions across the conductive polymer chains. The cycling voltage limitsare comprised between 1.5 V and 3.0 V with an average voltage of 2.25 V.The performance observed is comparable to that obtained in the precedingexample.

In conclusion, the particles according to the present invention presenta surprisingly notable spreading capacity, an excellent nominalcapacity, an excellent cycling stability and a remarkable high currentpower in electrochemical devices that use them, in particular at theelectrode level, as well as flexibility regarding electrode thicknessthat can be produced using these particles.

Thus at 12 C (5 minutes), the particles in nano form yield 90% of thenominal capacity, while the corresponding macroparticles develop no morethan 50% of the capacity. The macros also have a limitation withcurrents less then 5 C. The nano-particles do not have any limitation.

In addition, if the pretreatment of the initial mixture is notoptimized, e.g. if the milling time is less than 15 minutes, thesynthesis of the mixture in the presence of carbon gives rise tomacroscopic particles.

In addition, diffusion of lithium is faster in the case ofnano-particles.

Even though the present invention has been described using specificembodiments, it is understood that many variations and modificationscould be made to said embodiments, and the present invention covers allsuch modifications, usages or adaptations of the present invention thatgenerally follow the principles of the invention and including anyvariation of the present description which become known or areconventional in the field of activity wherein the present invention isused, and which can apply to the essential elements mentioned above, inagreement with the scope of the following claims.

The invention claimed is:
 1. A process for synthesizing, under anatmosphere of air, particles of an oxide corresponding to a formulaselected from: Li₄Ti₅O₁₂; Li_((4-α))Z_(α)Ti₅O₁₂, wherein α represents anumber greater than zero and less than or equal to 0.33, and Zrepresents at least one metal; and Li₄Z_(β)Ti_((5-β))O₁₂, wherein βrepresents a number greater than zero and less than or equal to 0.5, andZ represents at least one metal, said particles having carbon coatingwith a thickness in a range of 10-450 nm, said process comprising thesteps of: a) intimately dispersing ternary mixture of TiOx-LizY-carbon,wherein x is a number between 1 and 2, z is 1 or 2, Y is a radicalchosen from the group consisting of CO₃, OH, O and TiO₃ or a mixturethereof, and the carbon is a carbon powder selected from the groupconsisting of natural or artificial graphite, carbon black, Shawiniganblack, Ketjen black and cokes; b) heating the dispersion at atemperature of between 400 and 1,000° C.; and c) if appropriate, addinga source of at least one metal Z to the ternary mixture, wherein theoperating conditions are chosen in such a way as to yield a conversionof the initial products respectively into Li₄Ti₅O₁₂,Li_((4-α))Z_(α)Ti₅O₁₂, Li₄Z_(β)Ti_((5-β))O₁₂.
 2. The process of claim 1,wherein the dispersed ternary mixture is heated at a temperature ofabout 600° C.
 3. The process of claim 2, wherein the dispersed ternarymixture is heated in two steps, the first step being carried out untilthe dispersed ternary mixture reaches a temperature of about 400° C. andthe second step being carried out until the dispersed ternary mixturereaches a temperature of about 600° C.
 4. The process of claim 3,wherein the first step is carried out by rapid heating to around 400° C.5. The process of claim 3, wherein the second step is carried out byslow heating.
 6. The process of claim 3, wherein at least one step ofstep a) or step b) is carried out at least in part in inert atmosphere.7. The process of claim 1, wherein the dispersed ternary mixture isprepared using water and/or at least one solvent.
 8. The process ofclaim 1, wherein the dispersed ternary mixture is prepared withoutsolvent.
 9. The process of claim 1, wherein the Li_(Z)Y compoundcomprises at least one compound selected from the group consisting ofLi₂O, Li₂CO₃, and LiOH.
 10. The process of claim 9, wherein the Li_(z)Ycompound consists of Li₂CO₃.
 11. The process of claim 1, wherein thedispersed ternary mixture is prepared by high energy mechanical milling.12. The process of claim 1, wherein TiO_(x) is of the anatase or rutileTiO₂ type, or a mixture of both.
 13. The process of claim 1, wherein thecompound Li_(z)Y comprises Li₂TiO₃.
 14. The process of claim 1, whereinthe carbon is in the form of particles having a specific surface areagreater than or equal to 2 m²/g.
 15. The process of claim 12, whereinthe TiO₂ used as an initial product is coated with at least oneinorganic material.
 16. The process of claim 12, wherein the TiO₂ usedis coated with a hybrid inorganic-organic material.
 17. The process ofclaim 1, wherein the size of particles in the ternary mixture is between100 nanometers and 10 micrometers.
 18. The process of claim 1, whereinthe concentration of components of the ternary mixture are chosen insuch a way as to yield a conversion of the initial products into carboncoated Li₄Ti₅O₁₂, Li_((4-α))Z_(α)Ti₅O₁₂, Li₄Z_(β)Ti_((5-β))O₁₂.
 19. Aprocess for synthesizing, under an atmosphere of air, particles of anoxide corresponding to a formula selected from: Li₄Ti₅O₁₂;Li_((4-α))Z_(α)Ti₅O₁₂, wherein α represents a number greater than zeroand less than or equal to 0.33, and Z represents at least one metal; andLi₄Z_(β)Ti_((5-β))O₁₂, wherein β represents a number greater than zeroand less than or equal to 0.5, and Z represents at least one metal, saidprocess comprising the steps of: a) intimately dispersing ternarymixture of TiOx-LizY-carbon, wherein x is a number between 1 and 2, z is1 or 2, Y is a radical chosen from the group consisting of CO₃, OH, Oand TiO₃ or a mixture thereof, and the carbon is a carbon powderselected from the group consisting of natural or artificial graphite,carbon black, Shawinigan black, Ketjen black and cokes; b) heating thedispersion at a temperature of between 400 and 1,000° C.; and c) ifappropriate, adding a source of at least one metal Z to the ternarymixture, wherein the operating conditions are chosen in such a way as toyield a conversion of the initial products respectively into Li₄Ti₅O₁₂,Li_((4-α))Z_(α)Ti₅O₁₂, Li₄Z_(β)Ti_((5-β))O₁₂, each oxide having carboncoating with a thickness in a range of 10-450 nm.
 20. The process ofclaim 19, wherein the dispersed ternary mixture is heated at atemperature of about 600° C.
 21. The process of claim 20, wherein thedispersed ternary mixture is heated in two steps, the first step beingcarried out until the dispersed ternary mixture reaches a temperature ofabout 400° C. and the second step being carried out until the dispersedternary mixture reaches a temperature of about 600° C.
 22. The processof claim 21, wherein the first step is carried out by rapid heating toaround 400° C.
 23. The process of claim 21, wherein the second step iscarried out by slow heating.
 24. The process of claim 19, wherein thedispersed ternary mixture is prepared using water and/or at least onesolvent.
 25. The process of claim 19, wherein the Li_(z)Y compoundcomprises at least one compound selected from the group consisting ofLi₂O, Li₂CO₃, and LiOH.
 26. The process of claim 25, wherein the Li_(z)Ycompound consists of Li₂CO₃.
 27. The process of claim 19, wherein thedispersed ternary mixture is prepared by high energy mechanical milling.28. The process of claim 19, wherein TiO_(x) is of the anatase or rutileTiO₂ type, or a mixture of both.
 29. The process of claim 19, whereinthe carbon is in the form of particles having a specific surface areagreater than or equal to 2 m²/g.
 30. The process of claim 19, whereinthe size of particles in the ternary mixture is between 100 nanometersand 10 micrometers.
 31. The process of claim 19, wherein step b) ofheating the dispersion at a temperature of between 400 and 1,000° C.,occurs in an atmosphere of air.
 32. The process of claim 1, wherein stepb) of heating the dispersion at a temperature of between 400 and 1,000°C., occurs in an atmosphere of air.